Control system for hydraulic power transmission units



Aug. 13.71.940. E. CANNQ'N 2,211,406

GUN'I'ROL` SYSTEM FOR HYDRAULIC POWER lTRANSMISSION UNITS Filed July 28. 1936- 2 Sheets-Sheet 1 44 ELECTRIC Erl 6227122011 ATTORNEY E. CANNON 2,211,406

CONTROL SYSTEM FOR HYDRAULIC POWER TRANSMISSION UNITS Aug. 13. 1940.

2 Sheets-Sheet 2 Filed July 28, 1936 I INVENTOR Earl Gannon ATTORNEY lll'hl Patented Aug. 13, 1940 UNITED STATES PATENT OFFICE CONTROL SYSTEM FOR HYDRAULIC POWER TRANSMISSION UNITS Application July 28, l1936, Serial No. 92,990

8 Claims.

This invention relates to a hydraulic power transmission unit and the control system therefor.

It particularly relates to a system in which a reversible hydraulic motor is cyclically operated in either direction as required for a predetermined extent.

With liquid used as the power transmission fluid in my unit, its operation is quiet, smooth in acceleration and deceleration and at'all times under the control 4of the operator.

The pump and motor are preferably of the rotary piston type, the pump being driven continuously at constant speed with the hydraulic motor operating only when required. l

The smooth, yet positive, acceleration and deceleration of such a hydraulic power transmission unit from and to a given position is a serious problem due in part to the large inertia of the rotating portions of the hydraulic motor. The novel combination of means that I-teach takes care of this by so moving the controlling means as to produce the required acceleration. I relate the speed of the pump to that of the means governingl the action of the means controlling the rate of acceleration of thehydraulic motor.v In other words, the discharge rate of the main pump, or another moving with it, governs the speed of a piston that, either operates a bypass with a fixed stroke pump or alters the stroke of a variable discharge pump, either of which operations affects the discharge to the hydraulic motor in a predetermined manner.

A feature of this invention is the use of a by- 35 passing latch valve that bypasses the iiow of the pump except when the piston of the latch valve has been thrown off center by the action of either pilot valve connected to its respective end. The stopping of the motor at a predetermined position results from the action of timing means operated by the motor to remove the latches from functioning.

Another object of the invention is to provide interlocking means which act to prevent starting the device in operation by moving the wrong pilot, considering the intended direction of motion. In other words, my main aim is to provide a safe and foolproof whole.

Other features have to do with means for mechanically and hydraulically locking the unit in a predetermined position whenever it is not operating.

' Other features include the interlockv between the reverse valve which determines the direction CII (Cl. (iO-53) of motion, the timing means which stops the motion, and the pilots which start the unit.

' Further objects and features of my invention will be more, fully set forth in the specification and claims. 5

In the drawings:

Fig, 1 is a somewhat diagrammatic elevation.' y partially in section, of my invention when using a constant discharge pump.

Fig. 2 is a similar view, using a variable discharge pump.

Fig. 3 is a partial View similar to Fig. 1 showing valve 4 'and connections onan enlarged scale; Fig, 4 is a partial view similar to Fig. 1 showing valve 2`I and connections onanenlarged scale.

In Fig. 1, the piston for thelatch valve is provided with throttling grocves which are moved past the shut-off edge of a bypassing port at a predetermined rate; whilevin Fig. 2, the piston of the variable stroke adjuster of the pump is moved at. aV predetermined rate to increase-its discharge. In both cases this predetermined rate is related to the pump speed.

Description, Fig. 1

Referring to Fig, 1, the hydraulic circuit is as follows:

Oil is pumped from reservoir I by pump 2 into pressure line 3 connecting the pump with reverse valve 4. -When in neutral, this valve exhausts oil freely into exhaust line 5 to the reservoir. For gforward motion the oil pressure is connected with line 6, and for back motion with line 'I. Both lines 6 and 'I connect reverse valve 4 with latch valve 8. When the unit is not in operation', the oil is bypassed freely by latch valve 8 to the exhaust line 9. Lines 6 and 'I are also connected to holding valve III and thence by corresponding lines II and I2 to hydraulic' motor I3. Hydraulic motor I3 operates timing shaft III having an aixed disc I5 containing a positioning hole I6 for holding pin Il actuated by compound piston I8 of holding valve I0.

In holding valve I0, compound piston I8 is at all times acted upon by the pressure in lines 6 and I connecting Valve ="I0 to latch valve 8. Spring I9 resiliently opposes the motion of piston I8 due to such pressure so that piston I8 uncovers' the ports to lines 'II and I2 to hydraulic motor I3 only when such pressure is suflicient 50 to cause the operation of motor I3. Piston I8 is extended to form holding pin I I which is arranged adjacent to disc I5 affixed to timing shaft I4. The end of pin II is adapted to act as a brake on the face of disc I5 until it drops into hole I6. As shown, both hole I6 and the end of its holding pin I1 are made cylindrical, of slightly differing diameters, so as to definitely bring hydraulic motor I3 to within given limits of its predetermined position at the end of each cycle of operation.

Reverse valve 4 and timing shaft I4 are both operatively connected to latch valve 8'so that, when the reverse valve is in its fneutral position, neither latch 20 nor 2| can be engaged; and when the reverse valve is '1n-its forward position, the timing shaft can -notfaffect the backing latch 2 I; likewise, when the reverse valve is in its back position, the timing shaft can not affect the forward latch 20.

Latch valve 8 has piston 22 centered by springs 23. Between the two ends of piston 22 is a section of reduced area 24 for bypassing the fiow from lines E and 1 through. 9 whenever piston 22 is in its central position, and from either line 6 or 1 through 9 whenever piston 22 is not in its central position. Grooves 25 are provided to absorb the hydraulic shock otherwise occurring when the piston is moved away from its central, bypassing position. Pilots 26 and 21, respectively for causing lines 6 vand 1 to be effective, are connected as shown to the ends of latch valve 8. Admitting pressure to either end while the opposite end is connected with the exhaust will permit piston 22 to throw past latch 20 or 2| depending on whether either of the forward or back pilots 26 or 21 vis connected to pressure.

Interlock link 28 connects reverse valve 4 with latch valve 8 so that this reverse valve 4 dominates the action of the entire unit. Timing shaft I4 has rigidly mounted thereon spiral gears for driving the forward and back cams 29 and 30. 'Ihese are so adapted and arranged as to move respectively the latch trigger portions 3| and 32 in the proper direction. The longitudinal motion of the latches 20 and 2| is converted into a tilting motion of trigger portions 3| and 32.

Reverse valve 4 is connected by link 28 with levers having latch detent pins 33 and 34 respectively. The general arrangement of the mechanical link 28, trip cams 29 and 30, latch triggers 3| and 32 and detents 33 and 34 is such that the latches are positively held out when the reverse valve is in neutral and the back latch 2| is held out by'detent 34, acting against trigger'k32, away from cam 30 when the reverse valve is in its forward position; trigger 3| then being in the path of forward cam 29 and detent 33 being out of the way. When reverse Valve 4 is set in its back position, trigger 32 is in the path of cam 30, trigger 3| being held out of the path of forwardcam 29 by detent 33. Spring 35 is provided for each of latches 20 and 2| so that either latch is forced in behind piston 22 whenever this is drawn out of its centered, bypassing position. Spring-pressed trips 36 and 31 permit the cams 29 and 30 to be ineffective when striking their respective triggers 3| and 32 when moving in the opposite direction from that in which they must be effective.

Overruning valve 38 is provided in either of lines II or I2 (shown in line I2) between hydraulic motor I3 and holding valve I0. It consists of one spring loaded valve 39 having a spring 39a pressing on the top thereof, which engages at its upper end another valve 40 disposed in a valve seat formed in the upper wall of compartment 38a from which pipe I2 leads. Valve 40 is pressed upon at its top by a spring 40a, the pressure of which may be adjusted by a .will pass out through valve 40 into the main compartment of valve 38 and out through pipe 1. When the pressure on the motor falls below that of spring 40a, valve 40 will be closed. The motor therefore cannot continue to run at a pressure of liquid lower than the pressure of spring 40a. overrunning of the motor is therefore prevented by action of valve 40.` When the liquid is being supplied to motor I3 as stated, by pipe II, valve 39 will, of course, be held closed by the pressure of the liquid.

When the motor is being supplied with liquid from pipe 1 the same will pass into the main compartment of valve 38 and will pass upwardly through valve 39 into compartment 38a, through pipe I2 into the motor and will pass from the motor out through pipe II. The pressure of the liquid on top of valve 40 and the pressure of spring 40a will hold valve 40 closed. Valve 39 is lifted against the pressure of spring 39a. When the pressure in pipe 1 diminishes below that of spring 39a valve 39 will close and the motor will be prevented from running at a low pressure. Liquid cannot be supplied to the m0- tor at a pressure below that determined by spring 39a and overrunning of the motor at a pressure below that determined by spring 39a is thus prevented. Overrunning of the motor in either direction is therefore minimized. Valve 38 consequently minimizes overrunning of the hydraulic motor in either direction when latch valve 8 is in its bypassing position. When a biasing normal load exists, the spring on one valve is made stronger than that on the other so as to cause overrunning valve 38 to resist motion more strongly in thedirection of the load than in the opposite direction.

Pilot pump 4I is continuously driven by the same electric motor 42 as is main pump 2. These pumps respectively have pilot pressure relief valve 43 and main pressure relief valve 44 for limiting the maximum pressure by bypassing any flow above said pressure. Pilot relief valve 43 is preferably set at approximately pounds per square inch and operates continuously except for the small period of time when the pilots 26 and 21 are taking fluid. Pilot pump 4| is preferably of the gear type which gives a constant discharge rate so that piston 22 of latch valve 8 is operated at a definite speed as soon as either pilot is placed in its pressure position while the other remains in its exhaust position. In this way, the cushioning action of grooves 25 is most reliably related to the desired acceleration of hydraulic motor I3. On `the other hand, relief valve 44 for main pump 2 is preferably set to operate, with modern rotary piston-type pumps, at approximately 2000 pounds per square inch. This relief valve 44 preferably does not operate except when an excessive load is on the motor, relief valve 44 acting purely as a safety valve. However, when the load on motor I3 varies widely from tir* *'cipated in the design of cushioning grco pressure relief valve 44 may be set at a lov. .lu-e, say 1250 pounds per square inch, which will carry the load at speed and yet limit the acceleration to a desired value. In this case, it is apparent that pressure relief valve 44 will normally operate at least during the accelerating portion of each cycle of operation of hydraulic motor I3.

. tion, link 28 positions detent 34 to remove trigger Operation, Fig. 1

. hydraulic motor I3 can not turn as long as reverse valve 4 vis in neutral even though either pilot 26 or 21 be actuated to throw piston 22 of latch valve 8 away from its bypassing position. 'In addition, link 28, connected with reverse valve 4, holds latch detents 33 and 34 against latch triggers 3l and 32 so that latches 20 and` 2l are both held clear of piston 22 of latch valve 8 so that it cannot be latched as long as reverse valve 4 is in its neutral position.

With reverse valve 4 in its forward posi- 32 from the path of back cam 30. This ensures that latch 2I can not act to hold piston 22 of latch valve 8 in the event of an improper operation of back pilot 21. At the same time, link 28 positions detent 83 so that trigger 3| is in the path of forward cam 29. When both pilots 26 and 21 are in similar positions: either exhaust or pressure, piston 22 will have its bypass opening .24 connected simultaneously to .pressure lines 6 and 1 and to exhaust line 9. Further, .when back pilot-21 only is improperly brought to its pressure position thus throwing piston 22 away from its central position, the opening 24 will still leave pressure line 6 freely connected with exhaust line 9 so that no pressure can reach holding valve I to open it; consequently, hydraulic motor I3 can not operate under this' condition. However, when forward pilot 26 only is brought to pressure position, piston 22 of latch valve 8 is moved by the discharge from pilot pump 4I to gradually shut oil the bypassing connection between vlines 6 and 9,by the throttling grooves 25 so that pressure is applied to holding valve I0 through l pipe 6 and thence gradually to motor I3 by line II. At the same time, holding pin I1 is withdrawn from its position in hole I6 so that the motor starts smoothly and with the required acceleration as soon as this interlock is free. The motor willthen turn timing shaft I4 through one complete revolution of operation since forward cam 29 turns with timing shaft I4 andA strikes trigger 3| to remove latch 20 from behind piston 22 to thus permit spring 23 to center it, both pilots. 26 and 21 being in their exhaust positions,

so that the pressure from line 6 is bypassed freely back to exhaust line 9 which causes piston I8 of holding valve- I0 to stop hydraulic motor I3 and push holding pin I1 into positioning hole I6 on-disc I5 of timing shaft I4.

With reverse valve 4 in its back position, theoperation is as above described, under the forward position, except that the direction of operation of motor I3 and its timing shaft I4 are reversed. l

The operation of overrunning valve 38 has been made clear in its description.

`In rsumof its operation, my novel hydraulic power transmission unit operates in a thoroughly reliable and fool-proof manner: The hydraulic motor can operate only in the direction set by reverse valve 4; upon the operation of the wrong even though the proper pilot be depressed at the same time; hydraulic motor I3 stops smoothly and unfailingly at the proper position due to the mechanical braking action of the holding valve and the hydraulic braking action of the overrunning valve; in case the power supply from main pump 2 should fail between the ends of any cycle, hydraulic motor I3 would be braked both by the mechanical action of holding pin I1 against the side of disc I containing holding hole I6 andl .also braked hydraulically by the 'overrunning valve 38; and the operator has conf trol of the unitat all times since he can at any time stop hydraulic motor I3 immediately by bringing reverse valve 4 to its neutral position.

Description, Fig. 2

in service is improved by the fact that variable stroke pump operates to give a reduced discharge when hydraulic motor I3 is not operating, a great advantage in intermittent cyclical operation.

Stroke control valve 46 contains piston 41 normally centered by springs 48, preferably of the preloaded type as are springs 23 of latch valve 8. 35

Stroke control cylinder 49 on variable stroke pump 45 is connected by pressure pipe` 50 'to- 'valve 46 and to discharge line 9 from latch valve 8. The ends of valve 46 are connected respectively by lines 5I ando 52 with lines 6 and 1 connecting reverse valve 4 with vlatch valve 8. Pressure pipe 50 has a pressure relief valve 53 and contains a throttling valve 54 .so that the stroke control operates at an adjustable rate determined by the throttling of valve 54 relief valve 53 being set at, say, 300 pounds per square inch.- Since the operation of stroke control piston 56 against the opposing spring is Well-known in the art, a conventional showing is made to avoid distracting attention from the essence of my invention.

Further, in Fig. 2, line 5 from reverse valve 4 no longer exhausts directly to the reservoir but instead is connected to line 9 connecting latch Valve 8 and stroke control valve 46so that it can exhaust freely through line 51 to reservoir I only when piston 41 is thrown off center to an extreme position; at which time the pressure pipe 50 is also connected with exhaust line v51, thus'connecting stroke control cylinder 49 to atmospheric pressure.

When the hydraulic motor is not operating and with reverse valve 4 in neutral, the ilow from pump 45 passes through line 3,-reverse valve 4. line 5 and pressure pipe 50 'containing valve 54, and to stroke control cylinder 49 and relief valve 53 (limiting the maximum pressure that. opposes spring 55) so that piston 56 moves its full travel .in its cylinder 49 after which the reduced flow passes through relief valve 53 to reservoir I.

- l Operation, Fig. 2

'I'he operation of my improved device as shown y in Fig. 2 is generally as in Fig. 1 except for the changes incidental to the substitutionV of the variable stroke pump' 45 f or the constant discharge 'type pump 2 used in Fig. l. These changes are brought out in the following description of operation:

When reverse valve 4 or valve 8 is in neutral, the ilow therefrom passes through lines 5, 9, 6 and I so that the same pressure exists in lines 6I and 52 at opposing ends of stroke control valve 46. 'Ihis permits the centering springs 48 to center piston 41 so that the flow from 9 must bypass valve 46 through pressure pipe 50 to stroke control cylinder 49 and relief valve 53. This up-to-300 pounds per square inch pressure forces the stroke control piston 56 against its spring 55 to short-stroke the variable stroke pump 45 which then gives enough flow for operation of the latch valve 8 by either of pilot valves 26 or 21. Forward pilot 26 is shown depressed to a pressure position in Fig. 2, and the other pilot 21 being in exhaust position, piston 22 of latch valve 8 is thrown to an extreme position, thus permitting latch 20 to drop in behind piston 22 to retain it there after pilot 26 is restored to its normal exhaust position and until forward cam 29 strikes its trigger 3| to retract latch 20 from behind piston 22 of latch valve 8 and thus end the cycle of operation of motor I3. With reverse valve 4 in its forward position throwing the now through line 6, it is apparent that, as long as piston 22 is latched, the main flow must pass through line 6 to holding valve I and thus raise its piston I8 so that hydraulic motor I3 will operate. Also, fluid under this pressure passes through line I to throw piston 41' of stroke control valve 46 over to connect free exhaust 51 to the flow back from hydraulic motor I3 through line 1 and latch valve 8 and line 9; thus putting atmospheric pressure on line 52 to one end of valve 46, the full operating pressure being carried on its other end through line 5I as long as motor I3 is-operating.

'Ihis atmospheric pressure is likewise seen to be communicated to line 50 so that spring 55 forces piston 56 to move in the stroke control cylinder 43 to give full discharge from the variable stroke pump 45. The operation when the reverse valve is so set that the motor runs backwards is obvious from the foregoing.

The above-mentioned method of operation maintains a supply under pressure to the pilot valves at all times andalso makes the acceleration and deceleration of hydraulic motor I3 as smooth as possible. However, these apparent advantages are outweighed in general by the greater inherent simplicity and reliability of my preferred embodiment as shown in Fig. 1. Possible operatcbiections to the device of Fig. 2 are: full operating pressures are exerted on the pilot valves 'while motor I3 is in operation; there must be precise calibration of the centering springs in latch valve l and stroke control valve 46 for reliability of operation; and ilnally,iin the case of a biasing load on hydraulic motor I3, the operation of stroke control valve 46 may become unreliable except when an uneconomically high back pressure is set up by overrunning valve 38. The use of the embodiment shown in Fig. 2 is properly limited to permanent installations where no,

necessity exists for minimizing the weight of the unit.

While I have limited the showing of my in- Patent Re. 18,149 to Stratton) without departing from my teachings.

I claim:

1. In a hydraulic power transmission system containing a pump, a reversible motor and a uid-lled circuit operatively connecting them together, the combination of a valve insaid circuit between said pump and said motor for determining the direction of motion of said motor, latch valve means in said circuit between said reverse valve and said motor for governing the operation of said motor, holding valve means in said circuit between said latch valve and said motor actuated by thepressureinthesupplyline to said motor from said latch valve, and mechanical holding means for said motor including means for continuously biasing said holding means, said mechanical holding means being operatively connected to said holding valve so that upon a decrease in said pressure said holding means mechanically brakes said motor.

2. In a system as in claim 1, said holding valve being adapted to shut oil` at least one of the two lines of said hydraulic motor hydraulically to stop it.

3. In a system as in claim 1, said mechanical holding means being adapted to brake said motor lmechanically to bring it practically to a stop I within given limits of a predetermined position and said holding means being adapted to be actuated by said biasing means to retain said motor within said limits.

4. In a hydraulic power transmission system containing a uni-directional pump, a reversible motor anda fluid-filled circuit operatively connecting them together, the combination 0i a latch valve for bypassing the iluid from said hydraulic motor, two pilot means for actuating said valve to a latching position for either a forward or back direction of said motor, means for mechanically latching saidvalve in either of said positions, a reverse valve for determining the direction of motion of said motor, and a mechanical interlock connecting said reverse valve withr said latch valve kso that said latch valve can be latched only when the latch valve is operated by the proper pilot and not be latched lwhen the improper pilot is operated even though the proper pilot be simultaneously operated.

5. In a hydraulic power transmission system containing Va. uni-directional pump, a reversible motor and a fluid-filled circuit operatively connecting them together, the combination of a reverse valve, a iatchbypass valve in the lines of said circuit between said reverse valve and said hydraulic motor, said latch valve having an ex,- haust passing so that both of said lines and said exhaust passage are connected in a bypassing relation when said latch bypass valve is in a centered position, spring means for so centering said latch valve, pilot means for operating said latch valve from said bypassing position to the forward or to the back position when only the corresponding one of said pilot means is operated, and mechanical latching means adapted and arranged to latch said latch valve when it is moved to a position corresponding to the direction set by said reverse valve.

6. In a hydraulic power transmission system containing a uni-directional pump, a reversible motor and a fluid-filled circuit operatively connecting them together, the combination of a reverse valve for determining the direction of motion of said motor; a bypass latch valve for con-l trolling the supply of fluid to said motor; two pilot means each for actuating said latch valve from its bypassing position to cause the motor to operate in its respective direction, said latch valve including means for latching said valve in eitherl direction; timing means actuated by said motor and adapted to unlatch said valve to bring it to a bypassing position from either direction; and interlocking means connecting said reverse valve and said latch valve actuated by said reverse valve and arranged and adapted to prede termine which of said latching and unlatching means is operable according to the then position of said reverse valve. y

7. In a control system for a hydraulic power transmission unit having a duid-filled circuit operatively connecting a continuously operating pump and a motor that operates through a predetermined extent when required, the combination of a bypass valve in said circuit between said pump and said motor for bypassing said motor so that it is duid-actuated only when said bypass valve is closed and a holding valve connected to both lines of said circuit between said bypass valve and said motor and adapted to function upon a predetermined pressure in either of said lines between said holding valve and said bypass valve yto hydraulically hold said motor in its then position during at least a portion of the time said bypassing occurs.

8. In a control system Afor a hydraulic power vtransmission unit having a fluid-filled circuit operatively connecting a continuously operating pump and a motor that operates through a predetermined extent when required, the combination of a bypass valve in said circuit between said pump and said motor for bypassing said motor so that it is fluid-actuated only when said bypass v EARL CANNON.

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